I have a 14.5" AR that has the A2 front sight and a carry handle rear sight.
My understanding of sight in procedure calls for first zeroing at some close distance (depending on barrel length) using small aperture, with the rear elevation wheel set to 3/6. Then fine tune zero at 300 yard with the same setting. Once that's done, I can use the large aperture marked 0-2 for anything within 200 yard, and use small aperture in combination with the elevation wheel for 3,4,5,600 yard.
The only range I can normally shoot AR is ~20 yard, so I kept my rifle zeroed at 20 yard with small aperture. Last weekend I had the chance to shoot the AR at 100 yard. The group was shot using large aperture (0-2). It was about 11" high. Ammo used for both zeroing and 100 yard is Federal AE 223 55gr fmjbt.
By my calculation I was expecting group to be 6~7" high at 100 yard. I don't quite understand why it's 11" high. Here's my calculation:
55 gr @ 3050 fps (estimate from 14.5" barrel) with BC of 0.269, at sight height of 2.7", zeroed at 20 yard
Plug the above into calculator gave me a path of +8.9" at 100 yard.
I *think* the 0-2 aperture will result in POI lower than the small peep. I've heard it's about 2.5MOA on 20" barrel, so on 14.5" barrel it should be less than 2.5 MOA. By that, at 100 yard, the small peep will shoot +8.9" and the large peep should shoot around 8.9"-2.5", which is 6~7" high.
So my question is:
1. How can the 11" high group be explained?
2. Given my limited access to longer ranges (normally 20 but can occasionally shoot at 100 yard, what is the best way to sight in my iron sight?
My understanding of sight in procedure calls for first zeroing at some close distance (depending on barrel length) using small aperture, with the rear elevation wheel set to 3/6. Then fine tune zero at 300 yard with the same setting. Once that's done, I can use the large aperture marked 0-2 for anything within 200 yard, and use small aperture in combination with the elevation wheel for 3,4,5,600 yard.
The only range I can normally shoot AR is ~20 yard, so I kept my rifle zeroed at 20 yard with small aperture. Last weekend I had the chance to shoot the AR at 100 yard. The group was shot using large aperture (0-2). It was about 11" high. Ammo used for both zeroing and 100 yard is Federal AE 223 55gr fmjbt.
By my calculation I was expecting group to be 6~7" high at 100 yard. I don't quite understand why it's 11" high. Here's my calculation:
55 gr @ 3050 fps (estimate from 14.5" barrel) with BC of 0.269, at sight height of 2.7", zeroed at 20 yard
Plug the above into calculator gave me a path of +8.9" at 100 yard.
I *think* the 0-2 aperture will result in POI lower than the small peep. I've heard it's about 2.5MOA on 20" barrel, so on 14.5" barrel it should be less than 2.5 MOA. By that, at 100 yard, the small peep will shoot +8.9" and the large peep should shoot around 8.9"-2.5", which is 6~7" high.
So my question is:
1. How can the 11" high group be explained?
2. Given my limited access to longer ranges (normally 20 but can occasionally shoot at 100 yard, what is the best way to sight in my iron sight?
